Tschermak fractionation in calc-alkaline magmas: the Eocene Sabzevar volcanism (NE Iran)

  • Federico Lucci
  • Federico Rossetti
  • John Charles White
  • Hadi Shafaii Moghadam
  • Alireza Shirzadi
  • Mohsen Nasrabady
Original Paper

DOI: 10.1007/s12517-016-2598-0

Cite this article as:
Lucci, F., Rossetti, F., White, J.C. et al. Arab J Geosci (2016) 9: 573. doi:10.1007/s12517-016-2598-0

Abstract

Calc-alkaline arc magmatism at convergent plate margins is volumetrically dominated by metaluminous andesites. Many studies highlighted the importance of differentiation via fractionation processes of arc magmas, but only in the last decades, it has been demonstrated that not all rock-forming minerals may affect the evolution of calc-alkaline suites. In particular, a major role exerted by Al-rich hornblende amphibole as fractionating mineral phase has been documented in many volcanic arc settings. The aim of this work is to understand the role of the Tschermak molecule (CaAlAlSiO6) hosted in the hornblende and plagioclase fractionation assemblage in driving magma differentiation in calc-alkaline magmatic suites. We explore this issue by applying replenishment–fractional crystallization (RFC) and rare earth element–Rayleigh fractional crystallization (REE-FC) modeling to the Sabzevar Eocene (ca. 45–47 Ma) calc-alkaline volcanism of NE Central Iran, where hornblende-controlled fractionation has been demonstrated. Major element mass balance modeling indicates RFC dominated by a fractionating assemblage made of Hbl52.0–52.5 + Pl44.1–44.2 + Ttn3.3–3.9 (phases are expressed on total crystallized assemblage). REE-FC modeling shows, instead, a lower degree of fractionation with respect to RFC models that is interpreted as due to hornblende and plagioclase resorption by the residual melt. Calculations demonstrate that fractionation of the Tschermak molecule can readily produce dacite and rhyolite magmas starting from a calc-alkaline andesite source (FC = ca. 30 %). In particular, the Tschermak molecule controls both the heavy rare earth elements (HREE) and light rare earth element (LREE) budgets in calc-alkaline differentiation trends.

Keywords

Calc-alkaline magmatism Hornblende fractionation Tschermak Fractional crystallization modeling Iran 

Supplementary material

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Copyright information

© Saudi Society for Geosciences 2016

Authors and Affiliations

  • Federico Lucci
    • 1
  • Federico Rossetti
    • 1
  • John Charles White
    • 2
  • Hadi Shafaii Moghadam
    • 3
  • Alireza Shirzadi
    • 4
  • Mohsen Nasrabady
    • 5
  1. 1.Dipartimento di Scienze, Sezione Scienze GeologicheUniversità “Roma Tre”RomeItaly
  2. 2.Department of Geography and GeologyEastern Kentucky UniversityRichmondUSA
  3. 3.ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC ARC National Key Centre, Department of Earth and Planetary SciencesMacquarie UniversitySydneyAustralia
  4. 4.Science and Research BranchIslamic Azad UniversityTehranIran
  5. 5.Department of GeologyImam Khomeini International UniversityQazvinIran